Pneumatic dryers

ABSTRACT

In a pneumatic dryer having a vertical chamber through which the drying gas with the divided material in suspension therein flows upwardly, hot gas streams without divided material are injected tangentially into the chamber alternately in one and the other direction about the axis of the chamber. These streams may issue from a slotted central column. The gas entraining the divided material may be injected tangentially into the bottom of the chamber.

United States Patent 1 Mark [ 1 Feb. 5, 1974 PNEUMATIC DRYERS [76] Inventor: Andre Mark, 54, cours Lafayette,

Lyon, France 22 Filed: Jan. 26, 1973 21 Appl. No.: 326,962

[30] Foreign Application Priority Data Feb. 4, 1972 France 72.04761 [52] US. Cl. 34/10, 34/57 E, 34/57 A [51] Int. Cl. F26b 3/10 [58] Field of Search 34/57 R, 57 A, 57 E, 10; 432/l5, 58; 259/4 [5 6] References Cited UNITED STATES PATENTS 3,740,865 6/1973 Laguilharre 34/57 E 3,319,349 5/1967 Heinemann 34/57 E 3,049,343 8/1962 Helming 314/57 R 2,363,281 11/1944 Arnold 34/57 E 2,316,207 4/1943 Winter 34/57 E FOREIGN PATENTS OR APPLICATIONS 1,280,968 11/1961 France 34/57 R Primary Examiner-William F. ODea Assistant Examiner-W. C. Anderson Attorney, Agent, or Firm-Alexander & Dowell [5 7 ABSTRACT In a pneumatic dryer having a vertical chamber through which the drying gas with the divided material in suspension therein flows upwardly, hot gas streams without divided material are injected tangentially into the chamber alternately in one and the other direction about the axis of the chamber. These streams may issue from a slotted central column. The gas entraining the divided material may be injected tangentially into the bottom of the chamber.

11 Claims, 8 Drawing Figures Patented Feb. 5, 19 74 3, 789,513

5 Sheets-Sheet 1 Patented Feb. 5, 1974 3,789,513

5 Sheets-Sheet 2 Patented Feb. 5, 1974 3,789,513

- 3 Sheets-Sheet 3 A7 \f' 1 F J 2 1 PNEUMATIC DRYERS The present invention relates to the pneumatic drying of divided materials.

In pneumatic dryers the material to be dried is conveyed by a stream of a hot and dry gas in which it is suspended, this gas absorbing the moisture from the particles of the material. Since for obvious reasons the initial temperature of the gas is limited and since at any given temperature the transfer of the internal moisture from the particles to the gas is only progressive, the socalled residence time during which the particles are retained in suspension in the gas should be long enough. Moreover since the velocity of the drying gas stream cannot be lowered below a safe minimum beyond which the bigger particles would not be entrained, the path followed by the gas and divided material should be relatively long, in order to obtain the residence time required, which leads to cumbersome and expensive apparatus.

The length of the said path may be reduced by injecting hot and dry gas substantially free from divided material into the drying conduit at an appropriate distance from the inlet end thereotI The drying power of the gas is thus locally enhanced, and the drying operation is therefore more rapid.

It has already been proposed to cause the drying gas with the divided material in suspension therein to whirl within a drying chamber, such an arrangement increasing the residence time of the particles in the gas without requiring a drying conduit of great length.

According to the present invention a method for the pneumatic drying of a divided material in suspension in an ascending stream of drying gas within a substantially vertical chamber, consists in injecting into the said chamber and at successive levels along the height of the latter, additional drying gas streams substantially free from divided material, each directed substantially tangentially to a circumference co-axial to the said chamber, the said streams being alternately in one and the other direction about the axis of the chamber.

The ascending stream of drying gas with divided material in suspension therein is preferably obtained by injecting drying gas substantially free from divided material into the chamber through a lower non-tangential inlet and gas with divided material in suspension therein through a tangential inlet above the said lower inlet but below the lowermost of said successive levels.

The invention further concerns a dryer for the carrying into practice of the said method, this dryer comprising a substantially vertical and substantially cylindrical drying chamber, a central tubular column with closed upper end axially disposed within the said drying chamber, the said column defining an annular space between its periphery and the wall of the said chamber, and the peripheral wall of the said column being provided at successive levels along the height thereof with substantially vertical slots opening substantially tangentiallyto the periphery of the said column, the successive slots being directed alternately in one and the other direction about the axis of the said chamber, means for producing in the said annular space an ascending flow of drying gas with the divided material to be treated in suspension therein, between a lower inlet and an upper outlet of the said space, means for injecting a stream of drying gas substantially free from divided material into the open lower end of the said column, and means for separating the dried material from the gas issuing from the said drying chamber.

The means for producing an ascending stream of drying gas with the divided material to be treated in suspension therein preferably comprise a lower nontangential inlet in the said chamber, the said inlet being adapted to receive drying gas substantially free from divided material, and a tangential inlet disposed above the said lower inlet but below the lowermost one of said slots, the said tangential inlet being adapted to receive drying gas with the divided material in suspension therein.

In the accompanying drawings:

FIG. 1 is a view in elevation with parts in section, showing a pneumatic dryer according to the invention.

FIGS. 2 to 5 are cross-sections taken along lines Il- -II, III-III, IVIV and V-V of FIG. 1.

FIG. 6 is an enlarged fragmental cross-section illustrating a device for the adjustment of the operative cross-sectional area of the tangential slots.

FIG. 7 is a fragmental vertical section of a modification concerning the injection of drying air into the lower end of the central column.

FIG. 8 illustrates a modified embodiment of a dryer according to the invention.

In the embodiment of FIG. 1 the dryer comprises a vertical cylindrical drying chamber 1 having an upper and a lower frusto-conical ends, respectively 2 and 3.

The upper end 2 is connected by a lateral conduit 4 with the tangential inlet of a cyclone separator 5 of any conventional type, while the lower end 3 communicates axially with the outlet or high pressure side of a blower or fan 6 the inlet of which is connected with a conduit or flue 7, the latter receiving hot an dry gas from an appropriate generator. The hot gas conduit or flue is also connected with the inlet of another blower or fan 8 whose outlet or high pressure side is in turn connected with a conduit 9 which opens tangentially into the upper portion of the lower end 3 of the drying chamber 1, as indicated at 9a in FIG. 2. The inlet of blower 8 is provided with an appropriate device 10 through which the divided material to be dried may be introduced into the gas which flows into the blower. This device may be of any conventional description. It may for instance be realized in the form of a hopper associated with an air lock, or of a propelling screw in which the wet material forms a substantially air-tight mass.

A central tubular column 11 is axially disposed within the drying chamber 1. The closed conical upper end 11a of this column is connected with the upper end 2 of chamber 1 by means of arms such as 12, while its open lower end terminates within the lower end 3 of the said chamber, short of the frusto-conical wall thereof and at a level situated below the tangential outlet 9a of conduit 9. Column 11 thus defines between its outer periphery and the inner periphery of chamber 1 an annular space which has been referenced A, while its lower end leaves an annular passage between its outer edge and the wall of the lower end 3, a fine grid or wire mesh 13 (see FIG. 2) being disposed in this passage. This central column 11 comprises, starting from its lower end, a first cylindrical section 11b which is formed in its portion situated above the outlet 9a of conduit 9 with a slot opening substantially tangentially to the outer periphery of the column. In other words, and as shown in FIG. 3, the peripheral wall of the said upper portion is not perfectly cylindrical, but more or less spiral-shaped. It will further be noted from FIGS. 2 and 3, that considering the common vertical axis of chamber 1 and of column 11, slot 110 opens in the reverse direction with respect to the outlet of conduit 9 (counterclockwise for outlet 9a and clockwise for slot 11c). This cylindrical section 1 1b is followed by a frusto-conical section 1 1d of upwardly decreasing diameter which connects with a second cylindrical section 1 1e of lesser length or height than section 1 1b and of course of smaller diameter. This section He is also formed with a tangentially directed slot 11f (see FIG. 4) but which extends along the'full height of the said section. This slot is directed in the reverse direction with respect to slot 11c, i. e., counterclockwise. Section lle is followed by a second frusto-conical section 11g also of upwardly decreasing diameter, which is in turn followed by a third cylindrical section 11h closed by the upper end 11a above referred to, this third cylindrical section, of smaller diameter than section 1 12, but of greater length or height, also having in its lower portion a tangentially directed slot lli which opens clockwise, i. e., in the reverse direction with respect to slot 11f. It will be noted that the three slots 11c, 11f and 111' have substantially the same width and the same length.

Butterfly valves 14 and 15 are provided to act on the flow of hot gas respectively drawn by blowers 6 and 8 from the hot gas flue 7. Another rotary valve 16 is disposed in the lower end ofcolumn 11.

In operation hot and dry gas free from divided material is injected into the lower end 3 of the drying chamber 1 by blower 6. A minor portion of this gas flow passes through the grid or wire mesh 13 and rises through chamber 1, the major portion entering column 1 1. At the same time a flow of hot gas with the divided material in suspension therein is injected by blower 8 through the tangential outlet 9a of FIG. 2. The mixture of this tangential flow and of the ascending flow issuing from the grid or wire mesh 13 therefore rotates or whirls counterclockwise (as seen from above) within chamber 1 in the portion of space A which surrounds section 11b of column 11. But as soon as the gas and divided material reach the level of slot 110, they are submitted to the action of the tangential flow of hot gas which issues from the said slot and which rotates in the reverse direction, i. e., clockwise (see FIG. 3), and therefore the mixture of gas and meterial also whirls clockwise. The whirling motion is again reversed at the level of slot 11f and again at the level of slot 11g. Owing to the difference in the specific weight of the gas and of the particles of divided material, the successive accelerations and decelerations thus realized ensure an intimate stirring of the material through the gas, while at the same time the drying power of the latter is maintained at a sufficient level by the successive additions of hot and dry air issuing from the slots. The dried material is finally collected from the bottom of separator 5 in the usual manner, the wet and relatively cool gas exhausting through the upper outlet 17 of the latter.

Owing to the grid or wire mesh 13, the bigger particles of material are prevented from falling through the lower end 3 without having to increase the ascending velocity of the gas stream issuing from blower 6, which would of course reduce the residence time of the particles within the chamber.

As indicated at 18, an adjustable inlet of cool outer air may be provided, as for instance for reducing the temperature of the gas injected by blower 6 into the lower end of column 11.

The successive reductions in the diameter of column 11 are provided for taking into account the fact that the axial flow rate therein (i. e., the quantity of fluid flowing per unit of area through a transverse plane) de creases from its lower end to its upper end while conversely it increases in the annular space A. It is obvious that instead of being formed of successive cylindrical and frusto-conical sections, column 11 could be regularly frusto-conical along its full height. It should besides be remarked that while this decrease in the diameter of column 11 is convenient in many cases, it could be dispensed with in order to simplify the construction without any major inconvenience. In the case of a cylindrical column of uniform diameter, the drying chamber could be somewhat frusto-conical with an upwardly increasing diameter in order to take into account the progressive increase of the flow rate in the annular space A.

In the modification of FIG. 6 the slots such as 1 1c for instance, are adjusted in width by means of an angle iron 19 which is secured against the inner edge of the spiral-shaped cross-section of section 11b by means of rivets or bolts 20.

FIG. 7 illustrates another modification in which the annular passage provided between the lower end of column 11 and the frusto-conical wall of bottom 3 is adjustable by means of a sleeve 21 which may be fixed onto the periphery of the column at the height desired. With such a modification the grid or wire mesh 13 is preferably suppressed, the velocity of the gas through the annular passage being sufficient to prevent the bigger particles from falling therethrough.

Still a further modification (not illustrated) would consist in injecting into the upper end of column 11 a gas at a temperature different from the temperature of the gas issuing from blower 6. This may be of advantage in the case of materials which, when partially dried, are damaged by temperatures which they support in the wet state.

FIG. 8 illustrates an embodiment which is convenient in the case of materials which may support very high temperatures, at least in the wet state. With the embodiment of FIG. 1 the drying gas at an elevated temperature would have to flow through both blowers 6 and 8 and the latter should then be so constructed as to withstand such temperatures in normal operation, which would lead to a relatively expensive dryer. This is obviated in FIG. 8 by providing a single exhaust fan 22 having its inlet side connected by a conduit 23 with the outlet 17 of the cyclone separator 5. With such an arrangement the conduit 9 for the gas and divided material is directly connected with the hot gas flue 7, the material inlet device 10 opening into the said conduit. The bottom 3 of the drying chamber is connected with flue 7 by means of a laterally opening conduit 24 the butterfly valves 14 and 15 being respectively mounted in conduits 24 and 9, as shown. It is obvious that the operation of the dryer remains the same as in the case of the embodiment of FIG. 1, but the single fan 22 only receives relatively cool gas and has not therefore to be constructed for high temperatures.

1 claim:

1. In a method for the pneumatic drying of a divided material in suspension in an ascending stream of drying gas within a substantially vertical drying chamber having a substantially vertical axis and a given height, the improvement which consists in injecting into said chamber and at successive levels along the height of same, additional drying gas streams substantially free from divided material, each directed substantially tangentially to a circumference co-axial to said chamber, said streams being alternately in one and the other direction about the axis of said chamber.

2. In a method as claimed in claim 1, the step of obtaining said ascending stream of drying gas with divided material in suspension therein by injecting nontangentially into said chamber drying gas substantially free from divided material at a lower level situated below said successive levels, and by injecting tangentially into said chamber drying gas with divided material in suspension therein at a level situated between said lower level and said successive levels.

3. A pneumatic dryer for divided material comprismg:

a drying chamber having a substantially vertical axis and a given height, said chamber including a lateral wall and being formed with an upper outlet;

a central tubular column having a closed upper end,

an open lower end, and a peripheral wall, said column being disposed axially within said drying chamber with said peripheral wall defining an annular space with the lateral wall of said drying chamber, and said column having its peripheral wall formed with a succession of substantially vertical slots opening substantially tangentially to said peripheral wall at successive levels along the height of said chamber, the openings of said successive slots being alternately directed in one and the other direction about the axis of said chamber;

means to produce in said annular space an ascending stream of drying gas with divided material in suspension therein; means to inject a stream of drying gas substantially free from divided material into the open lower end of said column; and material separating means connected with the upper outlet of said chamber. 4. In a pneumatic dryer as claimed in claim 3, said means to produce an ascending stream of drying gas with divided material in suspension therein, comprising means to tangentially inject a stream of drying gas with divided material in suspension therein into said annular space below said successive slots.

5. In a pneumatic dryer as claimed in claim 4, said means to tangentially inject into said annular space a stream of drying gas with divided material in suspension therein directing said last-named stream in the reverse direction about the axis of said drying chamber with respect to the opening of the lowermost of said successive slots.

6. In a pneumatic dryer as claimed in claim 4, said column terminating downwardly short of the lateral wall of said drying chamber to leave an annular passage for a fraction of the drying gas substantially free from divided material, which is injected into the open lower end of said column.

7. In a pneumatic dryer as claimed in claim 6, a grid disposed in said annular passage to retain biggers particles of said divided material.

8. In a pneumatic dryer as claimed in claim 6, said column having a diameter which decreases from the lower end to the upper end thereof.

9. In a pneumatic dryer as claimed in claim 8, said column being formed of an alternate succession of cylindrical portions including said slots and of plain frusto-conical connecting portions.

10. In a pneumatic dryer as claimed in claim 3:

said drying chamber having a substantially axial lower inlet situated below the open lower end of said column;

said means to injects drying gas substantially free from divided material into the open lower end of said column comprising a first blower having its high pressure side connected with said lower inlet of said drying chamber;

and said means to tangentially inject into said annular space drying gas with divided material in suspension therein including a second blower independent from said first blower.

11. In a pneumatic dryer as claimed in claim 3, said means to inject drying gas substantially free from divided material into the open lower end of said column and said means to tangentially inject into said annular space drying gas with divided material in suspension therein, including a single exhaust fan connected to said separating means. 

1. In a method for the pneumatic drying of a divided material in suspension in an ascending stream of drying gas within a substantially vertical drying chamber having a substantially vertical axis and a given height, the improvement which consists in injecting into said chamber and at successive levels along the height of same, additional drying gas streams substantially free from divided material, each directed substantially tangentially to a circumference co-axial to said chamber, said streams being alternately in one and the other direction about the axis of said chamber.
 2. In a method as claimed in claim 1, the step of obtaining said ascending stream of drying gas with divided material in suspension therein by injecting non-tangentially into said chamber drying gas substantially free from divided material at a lower level situated below said successive levels, and by injecting tangentially into said chamber drying gas with divided material in suspension tHerein at a level situated between said lower level and said successive levels.
 3. A pneumatic dryer for divided material comprising: a drying chamber having a substantially vertical axis and a given height, said chamber including a lateral wall and being formed with an upper outlet; a central tubular column having a closed upper end, an open lower end, and a peripheral wall, said column being disposed axially within said drying chamber with said peripheral wall defining an annular space with the lateral wall of said drying chamber, and said column having its peripheral wall formed with a succession of substantially vertical slots opening substantially tangentially to said peripheral wall at successive levels along the height of said chamber, the openings of said successive slots being alternately directed in one and the other direction about the axis of said chamber; means to produce in said annular space an ascending stream of drying gas with divided material in suspension therein; means to inject a stream of drying gas substantially free from divided material into the open lower end of said column; and material separating means connected with the upper outlet of said chamber.
 4. In a pneumatic dryer as claimed in claim 3, said means to produce an ascending stream of drying gas with divided material in suspension therein, comprising means to tangentially inject a stream of drying gas with divided material in suspension therein into said annular space below said successive slots.
 5. In a pneumatic dryer as claimed in claim 4, said means to tangentially inject into said annular space a stream of drying gas with divided material in suspension therein directing said last-named stream in the reverse direction about the axis of said drying chamber with respect to the opening of the lowermost of said successive slots.
 6. In a pneumatic dryer as claimed in claim 4, said column terminating downwardly short of the lateral wall of said drying chamber to leave an annular passage for a fraction of the drying gas substantially free from divided material, which is injected into the open lower end of said column.
 7. In a pneumatic dryer as claimed in claim 6, a grid disposed in said annular passage to retain biggers particles of said divided material.
 8. In a pneumatic dryer as claimed in claim 6, said column having a diameter which decreases from the lower end to the upper end thereof.
 9. In a pneumatic dryer as claimed in claim 8, said column being formed of an alternate succession of cylindrical portions including said slots and of plain frusto-conical connecting portions.
 10. In a pneumatic dryer as claimed in claim 3: said drying chamber having a substantially axial lower inlet situated below the open lower end of said column; said means to injects drying gas substantially free from divided material into the open lower end of said column comprising a first blower having its high pressure side connected with said lower inlet of said drying chamber; and said means to tangentially inject into said annular space drying gas with divided material in suspension therein including a second blower independent from said first blower.
 11. In a pneumatic dryer as claimed in claim 3, said means to inject drying gas substantially free from divided material into the open lower end of said column and said means to tangentially inject into said annular space drying gas with divided material in suspension therein, including a single exhaust fan connected to said separating means. 